It was found in some aqueopus solutions that there are typically three regions in the single phase domain of the composition-temperature field, in each of which the mixing scheme is qualitatively different from those of other regions. In the water-rich region (I), the hydrogen bond strength of solvent H
2O is enhanced in the vicinity of a solute molecule, while the hydrogen bond prbability in the bulk away from a solute is reduced. The percolation nature of hydrogen bond network is still retained in this region (I) . In the intermediate region (II), the solution consists of two kinds of clusters rich in each component. Therefore the percolation nature is no longer present. In the solute rich region (III), the solute molecules cluster together and H
2O molecules are “adsorbned” on the surfaces of such clusters. The transition from the water-rich (I) to the intermediate (II) region is associated with anomalies in the third derivatives of Gibbs energy.
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